The present invention relates to an image processing device for determining an image area of image data obtained from an original by scanning, which is usable for digital copying machines, scanners and so on.
In conventional digital copying machines and scanners, image data inputted from an original through a CCD (Charge-Coupled Device) sensor or the like is subjected to processing for improving the image quality. For example, Japanese Laid-open Patent Publication (TOKKAI HEI) No. 4-188948 discloses an image processing device that discriminates a particular area of the image based on a feature extracted read-in image data and executes processing for further improving the quality of the image. According to this method, an average dispersion of differences of image data is determined relative to an average value obtained in a particular area of the image to discriminate the particular area as a character area if the average dispersion value is larger than the average value or as a halftone area if the average dispersion value is smaller than the average value, and the image processing is made adaptively to the discrimination result.
Japanese Laid-open Patent Publication (TOKKAI HEI) No. 4-270561 discloses another image processing device that sets two upper and lower thresholds Tb and Tc (Tb &gt;Tc), discriminates a particular area as a character area if the pixel density of the area is larger than the threshold Tb and smaller than the threshold Tc or as a halftone area if the pixel density is between Tb and Tc, and performs the image processing according to the discrimination result.
The former of the above-mentioned two image-discriminating methods involves a problem that the difference between an average dispersion value and an average value does not always sufficiently represent the feature of an image area and, therefore, may sometime make an error in discrimination of the image. This method may sometime have inadequate criteria and unsuitable average values as thresholds. Namely, further improvement of area discrimination accuracy is required.
The latter image discriminating method may reflect only a limited feature in the discrimination result since it discriminates an image area according to only two thresholds. Consequently, it cannot achieve a high accuracy discrimination of the image and have a high probability of misjudgment of the image, making it difficult to improve the image quality by further image processing.
Accordingly, the present applicant has proposed an image discriminating method which, as disclosed in Japanese Patent Application No. 8-238205, is free from the above-mentioned problems. Namely, this method estimates a feature value of a particular image area according to differences between optical densities of pixels neighboring to each other in horizontal and vertical directions in the area and discriminates the classification of that particular image area according to the feature value.
Therefore, the present invention has as its primary object the provision of an image processing device which can attain a further improved accuracy of discrimination of the classification of a particular image area to be processed for improving its quality.